Gas turbine engines are typically utilized to provide thrust to an aerial vehicle or mechanical power to drive an electrical generator. Gas turbine engines comprise at least a compressor, a combustion system, and a turbine, with the turbine coupled to the compressor through a shaft.
A typical compressor comprises a plurality of axially spaced and alternating rows of rotating and stationary airfoils. The rotating airfoils in the compressor are commonly referred to as blades and stationary airfoils are referred to as vanes or stators. Each stage of the blades and vanes decrease in radial height through the compressor as the volume of space decreases. As a result, the air compresses and pressure increases through each stage. The vanes serve to redirect the airflow onto the next stage of blades at the correct incidence angle.
Compressor vanes have an attachment for mounting the individual vanes in the compressor casing. The compressor blades are mounted by an attachment to the rotor while the compressor vanes are mounted by an attachment to the compressor casing. This configuration can be better understood with reference to FIG. 1, which depicts a portion of a typical gas turbine engine in cross section. The engine 10 includes an inlet 12, a compressor 14, a plurality of can-annular combustors 16, a turbine 18, a diffuser 20, and a shaft 22 (not shown) that lies generally coaxial to a centerline A-A. A closer, more detailed view of the compressor section 14 is shown in FIG. 2.
FIG. 2 depicts a series of alternating rows of blades 24 and vanes 26. The blades 24 are attached to a disk 28 and extend radially outward towards a compressor case 30 whereas the vanes 26 are attached to the compressor case 30 and extend radially inward towards the centerline A-A.
An example of a prior art compressor vane 26 used in the compressor 14 is shown in FIG. 3. The compressor vane 26 in FIG. 3 includes two straight hooks 32 located as part of the attachment 34 for mounting the vane 26 in the compressor case 30. However, the compressor case 30 is annular in shape and the slots 36 extend circumferentially about the case. Therefore, with the vane 26 having straight hooks 32 and the vanes being placed into circumferential slots 36 in the case, the hooks did not sit completely flush in the slots 36, and as a result a concentrated load occurs at the ends of the hooks 32.
This straight hook configuration is ideal for manufacturing due to its simple machining techniques and set-up required. Since all surfaces are straight and perpendicular, each vane can be individually machined. However, this arrangement is not ideal for engine operation due to the mismatch between the hooks and slots and the high localized stress that occurs due to this mismatch. As a result of this configuration the compressor vanes vibrate and rattle during engine operation. Any damping that does occur for this design is limited due to the stators being individual (low mass/low inertia) and having limited contact area with the slots for reacting displacement forces. As a result of the increased stress and limited damping, significant wear is exhibited at the compressor vane attachment hooks as well in the circumferential slot of the case. This wear requires premature replacement of the vanes and repair to the case.